Rotational molding, also known as rotomolding, is a molding process for creating many kinds of articles having mostly hollow components and typically made of plastic. Generally, a rotomolding process requires pulverized thermoplastic material to facilitate is proper melting of the material in a rotomold. For the pulverization process, a harder material is preferred because a softer material is difficult to pulverize or ground by standard processes. Therefore, materials for rotomolding are predominantly from the polyethylene family, for example, cross-linked polyethylene, low density polyethylene, linear low density polyethylene, high density polyethylene, and some other materials such as polyvinylchloride (PVC), platisols, nylons, and propylene.
Polyolefin-based elastomers, especially propylene-based elastomers, can be advantageously used in some applications, for example, articles having hollow components, including toys, cushion seats, recreational balls, pillows, and slides, because of the unique combination of elasticity, flexibility, and toughness from polyolefin-based elastomers. However, experience in rotomolding with pellets of propylene-based elastomers shows that voids and bubbles often appear in the rotomolded components.
There is a need for compositions of polyolefin-based elastomers, in particular propylene-based elastomers, in rotomolding, with improved properties to achieve good performance in elasticity, flexibility, and toughness.